Management and water quality of the Río Hondo reservoir and its tributaries

BAZÁN, RAQUEL; PILÁN, TERESITA; LARROSA, NANCY; GLATSTEIN, DANIEL; REUTER, FABIÁN; O'MILL, PATRICIA; MONARDE, FERNANDO; MURATORE, HÉCTOR; CERMINATO, FERNANDO; BORSELLINO, MARCELO; RODRÍGUEZ, ANDRÉS

Punta del Este, Uruguay

Conferencia; 6th Shallow Lakes Conference: Structure and Function of World Shalow Lakes; 2008

Facultad de Ciencias - Universidad de la República

The basin of Rio Hondo?s reservoir is exposed to degradation as consequence of industrial spills, untreated urban sewages drops and soil erosion. Particularly, a critical situation appears during the dry semester (May ? November), coincidental with the increase of the industrial activity. The lack of an adequate treatment of urban and industrial effluents, with the consequent increase of organic load, makes null the auto-purification possibility for the reservoir tributaries, during this mentioned dry period. As sewages and industrial effluents have their final destination in the reservoir, this waterbody acts as an extensive oxidation lagoon for organic elements, diminishing this way its tourist and fishing potential. With the aim of contributing to the planning for the management of the reservoir and its basin, seasonal monitoring campaigns at the reservoir and its tributaries were started in October 2006, conducted jointly by the National Universities of Santiago del Estero and Córdoba, with the collaboration of the Provincial Direction for Water and Reparation of Córdoba, and the financing of the National Subsecretary of Water Resources. The sampling sites were selected accordingly the proposed aims, the precedents and international standards ISO 5667/1. The adopted monitoring design included 17 sampling sites, 11 of which were in the reservoir, and the rest on its tributaries and different spills to the Rio Hondo reservoir.At each monitoring station, in situ measurements are done and water and/or sediment samples are collected for posterior laboratory analysis of nutrients and physical-chemistry and biological parameters. In the period of increasing industrial activity and decreasing precipitations, was observed that concentrations of P and N nutrients reached extreme values, even one magnitude order higher than other values observed for different eutrophic water bodies around the country. In addition, the organic matter indicators (TOC, BOD and COD) indicated a worrying situation at Gastona and Salí rivers, registering TOC values typical of waste water. A higher bacteriological contamination was observed at the northwestern tributaries. Every record of bacteriological parameters widely exceeded the guidelines for recreational uses at the Gastona and Salí rivers. The same behavior was shown by the Medina/Chico and Granero/Marapa rivers for Escherichia coli. Accordingly the obtained results, the Río Hondo reservoir classifies as a warm monomictic waterbody, with scanty transparence, hypereutrophied, with a decreasing oxygen concentration with the water depth, with algae and zooplankton genres which are indicatives for waters with a high load of organic components and that have the risk of harmful cyanobacterial blooms. This work constitutes the first systematic and periodic study of the Río Hondo reservoir, and allowed to obtain adequate information for a proper evaluation of its water quality and trophic classification. The results obtained from the information on nutrients conditions and contaminants in the tributaries and the reservoir, and the eutrophication response parameters allowed to optimize the current monitoring and to design a long-term one, in the framework of the Salí-Dulce Basin Committee activities.